Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene, propylene homopolymerizations, and their copolymerization

Abstract

A series of ethylene, propylene homopolymerizations, and ethylene/propylene copolymerization catalyzed with rac‐Et(Ind)2ZrCl2/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2‐thiophenecarbonyl chloride to label a 2‐thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene homopolymerization) and copolymer composition with time were also studied. [C*]/[Zr] strongly depended on type of monomer, with the propylene homopolymerization system presented much lower [C*]/[Zr] (ca. 25%) than the ethylene homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C*]/[Zr] of ethylene homopolymerization (ca. 70%). The chain propagation rate constant (kp) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 867–875

Quantification of active sites in single-site group 4 metal olefin polymerization catalysis

“…Similar discrepancies were identified for other metallocene based systems (e.g. 5a [58,92]). On the other hand, with the 5b/B(C6F5)3 system, very similar [C * ] values were obtained for polymerization of 1-hexene with different techniques [46,59,81].…”

“…an aromatic chromophore group [49]) in the close proximity to the active center may be detrimental to its regular performance, thus negatively influencing the kinetics of propagation. For the quench-labelling methods, the limited or sometimes poor selectivity of the reactions between the propagating metal-polymeryl species and the labeling reagent (CO [38,65,[76][77][78][79], O2 [85], Br2 [87], TCC [91,92] As evidenced from the investigations summarized in Part 4 of this review, a comprehensive critical analysis of the results presented here is largely hampered by the different conditions used. Also, as it is often difficult to apply strictly the same conditions with one technique of active sites count to another one, direct comparison of the same catalytic systems studied by different methods cannot be straightforwardly undertaken.…”

Kinetic and Thermal Study of Ethylene and Propylene Homo Polymerization Catalyzed by ansa-Zirconocene Activated with Alkylaluminum/Borate: Effects of Alkylaluminum on Polymerization Kinetics and Polymer Structure

“…It is obvious that the kinetic studies based on direct counting of the [C*]/[Z] concentration in the polymer reaction system can permit the easier construction of a comprehensive mechanistic model. Many such studies have been reported based on different procedures of counting the active center concentration in homogenous metallocene catalyzed polymerization [ 26 , 27 , 28 , 29 , 30 ]. However, conflicting results of active centers values have been found in the literature while dealing with the same type of metallocene catalyzed polymerization, maybe because of different sensitivity levels of the methods that have been used [ 26 , 31 , 32 ].…”

Facile synthesis of ethylene–propylene fully alternating copolymer and comparison with random copolymer of similar composition

“…[3][4][5][6] Ethylene-propylene copolymer with random comonomer sequence distribution has been synthesized by homogeneous vanadium catalysts or metallocene catalysts. [7][8][9][10][11][12][13][14][15][16][17] These copolymer and EPDM with ethylene content falling in the range of 50-60 mol % are produced in large scale and applied as synthetic rubbers for their low crystallinity and excellent elastomer properties. On the other hand, ethylene-propylene copolymerization with heterogeneous Ziegler-Natta catalysts like TiCl 4 /ID/ MgCl 2 type catalysts (ID 5 ester or ether) produces copolymer with very broad composition distribution.…”

“…Ethylene–propylene copolymer with random comonomer sequence distribution has been synthesized by homogeneous vanadium catalysts or metallocene catalysts . These copolymer and EPDM with ethylene content falling in the range of 50–60 mol % are produced in large scale and applied as synthetic rubbers for their low crystallinity and excellent elastomer properties.…”